1. Field of the Invention
The present invention relates in general to a magnetic transfer master medium provided on the surface thereof with protrusion portions formed in a pattern for transmitting data to a magnetic recording medium, and in particular to a magnetic transfer master medium for transferring data to a perpendicular magnetic recording medium.
Further, the present invention relates to a magnetic transfer method of employing the magnetic transfer master medium according to the present invention to transfer data to a perpendicular magnetic recording medium, and a magnetic transfer master medium forming method.
2. Description of the Related Art
Generally speaking, with regard to magnetic storage mediums, there is a demand for increased storage capacity and low cost. Further desired are so-called high-speed access mediums, which are capable of advantageously reading out the data of a desired location in a short time. Examples of these mediums include the high speed magnetic recording mediums (magnetic disk mediums) utilized in hard disk apparatuses and flexible disk apparatuses. So-called tracking servo technology, wherein the magnetic head accurately scans a narrow width track to achieve a high S/N ratio, plays a substantial role in attaining the high storage capacity thereof. A servo signal, address data signal, replay clock signal, etc., used for tracking within a certain interval occurring in one rotation of the disk are xe2x80x9cpreformattedxe2x80x9d, that is, recorded on the disk in advance.
Magnetic transfer methods realizing accurate and efficient preformatting, wherein the data such as a servo signal or the like borne on a master medium is magnetically transferred therefrom to a magnetic recording medium, have been proposed in, for example, Japanese Unexamined Patent Publication Nos. 63(1988)-183623, 10(1998)-40544, and 10(1998)-269566.
According to these magnetic transfer technologies, a master medium having an uneven pattern corresponding to the data that is to be transferred to a slave medium (a magnetic recording medium) is prepared. By bringing this master medium brought into close contact with a slave medium to form a conjoined body, and applying a transfer magnetic field thereto, a magnetic pattern corresponding to the data (e.g., a servo signal) borne on the master medium is transferred to the slave medium. The preformatting can be performed without changing the relative positions of the master medium and the slave medium; that is, while the two media remain stationary. Therefore not only is it possible to perform an accurate recording of the preformat data, it becomes possible to advantageously do so in an extremely short time.
However, as to the magnetic recording medium, two possibilities are longitudinal magnetic recording mediums provided with an easy magnetization axis in the horizontal direction in relation to the surface of the magnetic layer thereof, and perpendicular magnetic recording mediums provided with an easy magnetization axis in the vertical direction in relation to the surface of the magnetic layer thereof; however, in current practice, longitudinal magnetic recording mediums are generally employed, and the magnetic transfer technology described above has also been developed focusing mainly on the longitudinal magnetic recording mediums as the magnetic recording medium of choice. On the other hand, if a perpendicular magnetic recording medium is employed, an increase in data storage capacity can be expected in comparison to the longitudinal magnetic recording mediums.
For cases in which a magnetic transfer is performed on a perpendicular magnetic recording medium, a magnetic field must be applied in the perpendicular direction with respect to the surface of the magnetic layer thereof; wherein the optimal conditions differ in contrast to cases in which a magnetic transfer is performed on a longitudinal magnetic recording medium.
For example, when a magnetic transfer is performed to a perpendicular magnetic recording medium, the magnetic disorder is large at the border portions between the inverse magnetization portions and the uninverted magnetization portions, wherein a problem arises in that the signal quality is not favorable. Based upon the analysis by the inventors of the present invention, it has become clear that this problem is due to an insufficient constraint of the magnetic flux of the inverse magnetization portions, and is the cause of a reduction in signal quality.
Further, when a perpendicular magnetic transfer is to be performed, the thickness of the pattern of protrusion portions formed by the magnetic layer of the master medium is made thin. Because the magnetic pole distance generated to pass a magnetic field through vertically is short (diamagnetic field), and there is no assistance from adjacent protrusion portions in constraining the magnetic flux between protrusion portions, etc.; it is difficult to realize sufficiently favorable signal quality by providing a soft magnetic layer having a simple form.
The present invention has been developed in view of the forgoing circumstances, and it is an object of the present invention to provide a magnetic transfer master medium capable of performing a favorable magnetic transfer onto a perpendicular magnetic recording medium.
The magnetic transfer master medium according to the present invention is a magnetic transfer master medium comprising a substrate provided with a surface on which protrusion portions having a magnetic layer have been formed for transferring data to the magnetic layer of a perpendicular magnetic recording medium, wherein
the magnetic layer is also formed in the depression portions between the protrusion portions so that the magnetic layer formed on the protrusion portions and the magnetic layer formed in the depression portions are magnetically linked, and
the ratio of the thickness of said magnetic layer to the track direction width of the magnetic layer of the protrusion portions is greater than or equal to 0.8, and less than or equal to 3.
Here, the expression xe2x80x9ca surface on which protrusion portions having a magnetic layerxe2x80x9d refers to the portions protruding from base of the depression portions before the magnetic layer has been formed therebetween; wherein, a magnetic layer is formed over at least the tip portion of the these protrusion portions, and the protrusion portions themselves may be formed from the magnetic layer.
Further, the expression xe2x80x9care magnetically linkedxe2x80x9d refers to the passing through the magnetic layer of the protrusion portions of the greater part of the magnetic flux that passes through the magnetic layer of the depression portions when a transfer magnetic field is applied in the direction of the thickness of the protrusion portions; and does not refer to whether or not the magnetic layer has been formed as a continuous, connected layer over the protrusion portions and in the depression portions.
Further, the referent of xe2x80x9ctrack directionxe2x80x9d is the direction corresponding to the direction along the track formed on the slave medium by the magnetic transfer.
Note that it is advantageous, for example, that the transfer data be servo signals.
The magnetic transfer master medium according to the present invention is advantageously utilized in a magnetic transfer method wherein: the magnetic layer of the protrusion portions of said magnetic transfer master medium and the magnetic layer of the perpendicular magnetic recording medium are conjoined to form a conjoined body; and a transfer magnetic field is applied to said conjoined body in the direction perpendicular to the magnetic layer of said perpendicular magnetic recording medium so as to transfer the data from the master medium to the magnetic layer of said perpendicular magnetic recording medium. Here, the referents of xe2x80x9cconjoinedxe2x80x9d include not only to the state wherein the respective surfaces of both of said mediums are in complete close contact with each other, but also states wherein said mediums are disposed in a state wherein a uniform interval is maintained between the respective surfaces thereof. The vertical recording medium, more specifically, can be a discoid magnetic recording medium such as a hard disk, a flexible disk, or the like.
Further, the magnetic transfer master medium according to the present invention is a magnetic transfer master medium comprising a substrate provided with a surface on which protrusion portions, which form a pattern, having a magnetic layer have been formed for transferring data to the magnetic layer of a perpendicular magnetic recording medium, wherein
it is desirable that the magnetic layer is formed while a magnetic field is applied to the substrate in the direction perpendicular to the surface thereof.
At this time, the direction in which the magnetic field is applied when the magnetic layer is to be formed is substantially parallel to the direction in which the transfer magnetic field is applied when a magnetic transfer is to be performed; the orientation thereof can be in the same direction, or in the opposite direction. The easy magnetization axis of the magnetic layer is the direction substantially perpendicular to the surface of the master medium, and perpendicular magnetic anisotropy is given to the magnetic layer by the application of the magnetic field during the formation thereof.
Further, the magnetic transfer master medium according to the present invention is a magnetic transfer master medium comprising a substrate provided with a surface on which protrusion portions formed in a pattern having a magnetic layer has been formed for transferring data to the magnetic layer of a perpendicular magnetic recording medium, wherein
it is desirable that a second magnetic layer having an easy magnetization axis parallel to the easy magnetization axis of the magnetic layer, and a coercive magnetic force larger than that of said magnetic layer is provided between the protrusion portions.
At this time, the second magnetic layer can be formed in the depression portions between the protrusion portions so as to completely fill in said depression portions, or can be formed in only a portion of the depression portions between the protrusion portions, as long as it is formed between the protrusion portions.
It is desirable that the second magnetic layer is magnetized in the opposite direction to initialized field in advance.
The phrase xe2x80x9cperpendicular directionxe2x80x9d refers to the direction perpendicular to the surface of the master medium. That is to say, the easy magnetization axis of the magnetic layer and the second magnetic layer are perpendicular to the surface of the master medium; the second magnetic layer is magnetized unidirectionally in said perpendicular direction in advance.
It is desirable that the coercive magnetic force of the second magnetic layer is approximately twice as large as that of the perpendicular magnetic recording medium. Note that with regard to the magnetic transfer master medium according to the present invention, it is preferable that the magnetic layer formed on the surfaces of the protrusion portions be of either a soft magnet or a semi-hard magnet.
According to the magnetic transfer master medium of the present invention: by making the ratio R between the cross-sectional height (i.e., the thickness of the magnetic layer) of the magnetic layer of the protrusion portions and the track direction width of the magnetic layer of the protrusion portions greater than or equal to 0.8 and less than or equal to 3.0, the signal quality can be improved by raising the effect of the attraction of magnetic flux the toward the magnetic layer of the surface of the protrusion portions, and signal omissions can be prevented, whereby a favorable magnetic transfer can be performed onto a perpendicular magnetic recording medium. If the ratio R is less than 0.8, the inverse magnetic field generated within the magnetic layer when a transfer magnetic field is applied in the direction of the cross-sectional height becomes larger, the attraction of the magnetic flux by said magnetic layer becomes deficient, and signal quality is reduced thereby. On the other hand, if the ratio R is greater than 3.0, damage to the surface of the magnetic layer of the surface of the protrusion portions becomes remarkable, and the contact deficiencies caused by said damaged pieces, or the transfer deficiencies due to signal deficiencies or the like caused by said damage occur.
Further, by the formation of the magnetic layer on not only the surface of the protrusion portions but on the depression portions between the protrusion portions as well, wherein the magnetic layer formed over the protrusion portions and the magnetic layer formed in the depression portions are magnetically linked, the attraction of the magnetic flux toward the magnetic layer of the surface of the protrusion portions is facilitated, and a favorable magnetic transfer can be performed.
Still further, according to the magnetic transfer master medium of the present invention: if the magnetic layer of the pattern of protrusion portions of the magnetic layer formed on the surface of the master medium is a magnetic layer that is formed while a magnetic field is applied in the direction perpendicular to the surface of the substrate, because this magnetic layer itself is thereby given perpendicular magnetic anisotropy by this magnetic field, the effective magnetic quantity of the magnetic layer due to the inverse magnetic field occurring when the master medium has been conjoined with a slave medium and a transfer magnetic field is applied to perform the magnetic transfer becomes larger, and the effect whereby the magnetic flux is attracted toward the magnetic layer of the surface of the protrusion portions is increased, the constraint of the magnetic flux can be improved, and the magnetic disorder at the border portions of the inverse magnetic fields and uninverted magnetic fields can be suppressed; whereby, the signal quality can be improved and a favorable magnetic transfer can be performed onto a perpendicular magnetic recording medium.
In addition, according to the magnetic transfer master medium of the present invention: if the interval between the protrusion portions of the surface of the master medium, which are provided with a magnetic layer, is provided with a second magnetic layer that has an easily magnetized axis parallel to that of the magnetic layer, and a coercive magnetic force larger than that of said magnetic layer, a second magnetic layer having a large coercive magnetic force and which has been magnetized in the direction opposite that in which the transfer magnetic field is to be applied can be used when the magnetic transfer is to be performed; by magnetizing the magnetic field in advance as described above, the effect whereby the magnetic flux is attracted toward the magnetic layer of the surface of the protrusion portions is increased, and the magnetic disorder at the border portions of the inverse magnetic fields and uninverted magnetic fields can be suppressed; whereby, the signal quality can be improved and a favorable magnetic transfer can be performed onto a perpendicular magnetic recording medium.
If the data borne by the magnetic transfer master medium of the present invention is, for example, servo signals, a favorable transfer of the servo signals can be easily performed onto a perpendicular magnetic recording medium; whereby preformatted perpendicular magnetic recording mediums can be manufactured efficiently.
According to the magnetic transfer method of the present invention: the magnetic transfer master medium of the present invention is conjoined with a perpendicular magnetic recording medium to form a conjoined body; and a transfer magnetic field is applied to said conjoined body in the direction perpendicular to the track surface of said perpendicular magnetic recording medium to transfer data to said perpendicular magnetic recording medium; wherein, as described above, because the attraction of the magnetic flux toward the soft magnetic layer of the surface of the protrusion portions is favorable, a favorable magnetic transfer can be performed.
Note that a perpendicular magnetic recording medium onto which a magnetic transfer has been performed according to the magnetic transfer method described above employing the magnetic transfer master medium of the present invention is a recording medium provided with a favorable data signal; for cases in which the transfer data is servo signals, in particular, recording and playback quality is improved due to the increased accuracy in the positioning of the magnetic head.